1. Field of the Invention
The present invention relates to an aging drive method for thin film EL panels which includes a group of transparent electrodes, a group of metal electrodes disposed thereover and extending in a direction so as to intersect the group of transparent electrodes, and an EL emitting layer interposed between the two groups of electrodes to provide picture elements at the respective intersections. The method is especially useful for thin film EL panels of a large area.
2. Description of the Prior Art
Thin film EL panels are generally aged for a specified period of time following the preparation of the thin film by applying an alternating voltage to the picture elements positioned at the intersections of a group of transparent electrodes and a group of metal electrodes, for example. This is done to stabilize the variations in the luminescence brightness, etc. which occur with time and further to reject a faulty device due to an initial malfunction.
As disclosed in U.S. Pat. No. 4,412,155 granted to the present applicant and in U.S. Patent Application Ser. No. 06/401,385 filed on July 23, 1982 by the present applicant and now U.S. Pat. No. 4,818,913, the EL panel is aged by applying alternating voltage pulses across the group of transparent electrodes, which are all short-circuited, and the group of metal electrodes, which are all shortcircuited, to cause all the picture elements to luminesce simultaneously. Further, the procedure is repeated over a specified period of time.
However, when the above aging method is used for a thin film EL panel having a large area, the waveform of the alternating voltage pulses applied to the picture element involves a time lag which is needed for the voltage to reach a definite level, i.e. so-called waveform rounding. This owes to the time constant which is dependent on the resistance of the transparent electrode, and the capacitance of the picture element. The method is therefore unable to age all the picture elements uniformly.
This problem can be overcome by dividing the metal electrodes, which are arranged in parallel, into a group of odd-numbered electrodes and a group of even-numbered electrodes, and applying a voltage across the two groups.
This method is free from the influence of a time constant due to the resistance of the transparent electrodes. This is because the picture elements of the group of odd-numbered metal electrodes are connected in series with the picture elements of the other group, through the transparent electrodes.
Nevertheless, if a dielectric breakdown occurs in a small number of picture elements during this method, a voltage drop at the faulty picture elements is added to the other faultless picture elements. This results in great voltage pulse exceeding the voltage pulse needed for aging being applied to the faultless picture elements to induce a further dielectric breakdown. This is because the group of faulty picture elements is connected in series with the group of faultless picture elements.